This application will develop magnetic resonance imaging (MRI) criteria to predict outcome of thrombolysis after focal cerebral embolic ischemia in rats. The goal of this proposal is to assess whether the MRI measurements can identify reversibly damaged tissue and identify cerebral tissue that is destined to hemorrhage when treated with a thrombolytic agent. The applicants would also investigate whether the efficacy of thrombolytic intervention can be characterized and predicted by quantitative changes in MRI measurable parameters. Two specific aims are proposed: Specific Aim 1-To predict hemorrhagic transformation (HT) after embolic stroke and thrombolysis in rats using MRI. Specific Aim 2a-To identify reversibly damaged ischemic tissue after embolic stroke and thrombolysis in rat using MRI. Specific Aim 2b B To determine the ability of MRI to predict the efficacy of thrombolytic intervention with rt-PA. The applicants would employ multimodality MRI and image analysis methodology in combination with histological endpoints to characterize cerebral tissue subjected to embolic stroke and to predict outcome of thrombolytic therapy. The long-term goal is to provide new and important information relevant to the treatment of acute stroke by thrombolysis.